1. Field of the Invention
The invention relates to a lighting device comprising a side-emitting light guide. More particularly, the invention relates to a lighting device that comprises an LED and in which the light from the LED is injected into a side-emitting fiber bundle. Such lighting devices are applied especially in the automotive sector as an ambience lighting. The invention further relates to a sleeve that is used to terminate a side-emitting fiber bundle and to inject the light from an LED into the fiber bundle.
2. Description of Related Art
Lighting devices with side-emitting light guides are known from practice. These are in particular lighting devices in which the light from a semiconductor light source, in particular an LED, is injected into a bundle of side-emitting glass or plastic fibers. Basically, a light guiding fiber is mostly made up of a light-guiding core that is surrounded by a covering material (cladding) of a lower refractive index.
At the core-cladding interface, total reflection occurs so that the light is guided along the fiber. For emitting light laterally along an extended length, for lighting applications, side-emitting fibers are known in which the light-guiding core includes scattering particles, for example, or in which the cladding includes defect sites at which the light is emitted sideways. Such side-emitting light guides in particular consist of a glass fiber bundle inserted in a plastic tube. Such a glass fiber bundle inserted in a tube is flexible and can for example be installed in a vehicle as an ambient lighting. In this case, the LEDs are usually accommodated in a housing from which the glass fiber bundle inserted in a tube extends into the vehicle.
For injecting the light from the LEDs into the fiber bundle, it has been known to embed the end of the fiber bundle in a covering material which is cured. Then, the end of the wrapped fiber bundle is cut off and polished, so that a light entrance surface is created. This procedure is very cost and time consuming.
German patent DE 10 2008 044 938 B4 (Schott AG), by contrast, provides a method in which light guiding fibers are inserted into a sleeve which is filled with an adhesive. The adhesive is cured and the light is injected into the fiber cores through the transparent adhesive.
However, for side-emitting ambiance lighting it has been found that inhomogeneities in the color distribution of the light occur.
This particularly applies to the case in which the employed light source is a so-called RGB light source. Such light sources are for example implemented as an LED chip. In this case, three LEDs of different colors are arranged close to each other on the chip.
In conventional injection methods, the light from these LEDs will be injected into the individual fibers with different intensity. These inhomogeneities in intensity distribution, in turn, combine with the usually existing inhomogeneities of the proportion of light that is emitted sideways.
Even small color changes are perceived by the human eye.